Abstract
The three-dimensional network of lacunae and canaliculi that regulates metabolism in bone contains osteocytes and their dendritic processes. We constructed a synchrotron radiation X-ray microscope for sequential tomography of mouse tibia first by using a Talbot interferometer to detect the degree of bone mineralization and then by using absorption contrast under a slightly defocused setting to enhance outline contrast thereby visualizing structures of the osteocyte lacuno-canalicular network. The resultant pair of tomograms was precisely aligned with each other, allowing evaluation of mineral density in the vicinity of each osteocyte lacuna and canaliculus over the entire thickness of the cortical bone. Thus, multiscan microscopic X-ray tomography is a powerful tool for analyzing bone mineralization in relation to the lacuno-canalicular network at the submicron resolution level.
Highlights
Bones provide structural support for the body and store biominerals such as calcium and phosphate in the form of hydroxyapatite crystals, which are integrated into organic bone matrix consisting of collagen fibers and other bone matrix proteins
We constructed a synchrotron radiation X-ray microscope for sequential tomography of mouse tibia first by using a Talbot interferometer to detect the degree of bone mineralization and by using absorption contrast under a slightly defocused setting to enhance outline contrast thereby visualizing structures of the osteocyte lacuno-canalicular network
Multiscan microscopic X-ray tomography is a powerful tool for analyzing bone mineralization in relation to the lacuno-canalicular network at the submicron resolution level
Summary
Bones provide structural support for the body and store biominerals such as calcium and phosphate in the form of hydroxyapatite crystals, which are integrated into organic bone matrix consisting of collagen fibers and other bone matrix proteins. A subset of osteoblasts embeds itself within newly formed bone matrix and differentiates into osteocytes in osteocytic lacunae. Osteocytes are the most abundant cells in mammalian bone [2]. Osteocytes extend numerous dendrites into canaliculi within bone matrix and maintain osteocyte-osteocyte interactions through gap junctions at the tip of dendrites. Proposed functions of the lacuno-canalicular network include sensing of mechanical load, detection of microfractures, transport of nutrients and waste to and from osteocytes, and, most remarkably, delivery of osteocyte-derived bioactive proteins, such as sclerostin, an inhibitor of osteoblast function, and receptor activator of NF-κB ligand (RANKL), a critical activator of osteoclast differentiation, to the bone surface. Uncertainties remain regarding the direct roles of osteocytes, in particular, osteocytic canaliculi, in bone mineral metabolism
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